This invention relates generally to a specimen image display apparatus for use in a scanning electron microscope or similar type instrument, and more particularly to a charged particle beam scanning apparatus for facilitating changeover from an initially displayed specimen image to a desired field of view of said specimen image.
In an apparatus having a scanning function, such as a scanning electron microscope, an electron beam exposure device or the like, the electron beam irradiates and scans over a selected area of the specimen surface, the signal resulting from said electron beam irradiation being used as a brightness modulation signal for an image display means synchronized with said scanning electron beam. The magnification and field of view of the specimen image displayed on said display means depends on the extent and position of the electron beam scanning area on the specimen surface. Accordingly, it is necessary to adjust the electron beam deflecting (scanning) signal and/or the specimen goniometer stage (including shifting, rotating, and tilting mechanism) in order to irradiate the desired area on the specimen surface with the electron beam. This involves determining the desired field of view using a low magnification image, adjusting the electron beam scanning signal and/or specimen goniometer stage so as to display the desired point (small area) on the low magnification image at the approximate center of the viewing screen, and reducing the magnitude or amplitude of the scanning signal so as to display a higher magnification image on the viewing screen. Generally, the above procedure has to be repeated several times in order to observe the desired field of view, which makes it time consuming and troublesome. Particularly, it is very difficult to manually operate the specimen goniometer stage smoothly and precisely. In order to eliminate this difficulty, a beam scanning device for controlling the image shift and rotation electrically without operation of the shifting and rotating mechanism of the specimen goniometer stage is used. However, the electrical image shifting function and the electrical image rotating function of the conventional scanning device cannot be used at the same time, because these functions are interdependent.
It is therefore an object of this invention to provide an improved scanning device in which the image shifting function and the image rotating function are incorporated independently to each other.
Another object of this invention is to provide an improved scanning device for selecting the field of view of the specimen image quickly and precisely.